1. Field of the Invention
The present invention pertains to a guide and shield device which is attachable to the lower end of a new drivepipe for an offshore well so that the new drivepipe may be driven alongside the stub end of a previous drivepipe.
2. Background
In the drilling of offshore oil and gas wells, in particular, a conventional technique involves driving a relatively large-diameter pipe into the sea floor to form a structure through which the well may be drilled and completed. This casing or so-called "drivepipe" may encounter a subterranean blockage or other impediment to being driven to a sufficient depth to support the well, or the drivepipe may otherwise be damaged or a slot may need to be reclaimed for a production platform. In some instances a deflector or so-called whipstock is installed on top of the first drivepipe so that a second drivepipe may be guided in the direction that the well is to be drilled.
If the original drivepipe is to be abandoned, it is usually cut off below the sea floor and the whipstock is connected to the lower end of the new drivepipe and stabbed into or over the top of the old drivepipe to form the guide for the new drivepipe. One example of a whipstock for the above type of operation is described in U.S. Pat. 4,733,732 to Samuel C. Lynch and assigned to the assignee of the present invention. Although a whipstock as described in the '732 patent is advantageous for certain applications, it is often difficult to properly stab the whipstock into or sleeve it over the stub of the old drivepipe. In particular, in offshore well operations it is very difficult to positively stab the whipstock spear in the old drivepipe or casing which has been abandoned and which is required to be located off of so that the new drivepipe will proceed in the proper direction. If a whipstock is not correctly located, it is also difficult to retrieve or "fish" it out of the wellbore, particularly if the drivepipe to which the fishing tool is connected is extended through the collarlike guides which are often used to guide drivepipe with respect to a platform structure or a subsea template. These guides are commonly used to centralize or locate drivepipe with respect to the platform or the desired location of the well.
Still another problem in using whipstocks, including the type described in the '732 patent, is the tendency for the lower end of the whipstock or the new drivepipe to which it is connected to encounter debris lying on the sea floor around the old drivepipe stub. Particularly, in installing new drivepipe in wells which have been damaged due to destruction or damage of the drilling platform, a great deal of debris may lie on the sea floor in and around the old drivepipe. The open end of the whipstock guide or the drivepipe to which it is connected will cause the new drivepipe or the whipstock to "swallow" the debris while it is being driven. This results in improper guidance of the new drivepipe and possibly added time to clean out the newly driven pipe, if such cleanout is even possible.
Accordingly, there has been a need to develop a new technique and device for guiding drivepipe to recover a so-called well "slot" and install a well directly adjacent to or essentially in the same vicinity of an abandoned drivepipe structure or the like. It is to this end that the present invention has been developed.